This invention relates to characterising the spatial relationships of objects around robots, for example surgical robots.
Some surgical robots are of considerable bulk and comprise multiple surgical arms stemming from a single fixed or mobile base. In these systems the fact that the surgical arms are mechanically attached to a common base means that the spatial relationship between the arms is inherent and can readily be established through knowledge of the arms' configurations. However, these systems are bulky, making them difficult to move into place in an operating theatre. Also, the range of possible spatial relationships between the arms is limited by the fact that the arms stem from a single base, and this restricts the range of surgical procedures that can be carried out by such systems.
FIG. 1 illustrates three separate surgical robots 1, 2, 3 each having a respective arm. The robots are positioned in preparation for performing surgery on a patient 4 who is on an operating table 5. The robots are communicatively linked to a control station 7 from where they can be operated by a surgeon. In this example robot 3 is fixedly mounted to the ceiling of the operating theatre. Robots 1 and 2 are mounted on mobile carts 8, 9. The carts are equipped with lockable wheels so that they can be pushed into place by a technician before surgery begins and then fixed in place for the duration of the operation. The table on which the patient lies is also on lockable wheels. The patient can be prepared for surgery outside the theatre and then moved into the operating theatre on the table. This flexibility of positioning of the patient and the robots has the advantage that the equipment can perform a greater range of procedures than some other robot systems. However, it has the consequence that after the table and the carts 8, 9 have been moved into place the relative positions of the bases of the arms 1, 2, 3 are essentially unknown, as is their relationship to the table 5 on which the patient is resting.
The spatial relationships between the arms would be useful information for the control station 7. It could, for example, be used to avoid collisions between the arms.
One way to establish the spatial relationships between the arms would be to provide a set of jigs or floor markings that are used by the technician to set the positions of the robots' carts and/or the patient's table. The spatial relationships between the apparatus would then be known. However, very many such jigs or markings would be needed to provide for the full range of surgical procedures.
Another way to establish the spatial relationships would be for the technician to measure the distances between datum points on the arms and the table and to input that data to the control system. This is time-consuming because to fully characterise the spatial relationships in three dimensions many such measurements would be needed, and there is the possibility that errors might be made in taking the measurements or entering them in.
There is a need for an alternative way of establishing the spatial relationship between robots, particularly surgical robots.